Blood platelets play a critical role in the prevention of excessive blood loss at sites of tissue injury. They are formed from megakaryocytes in the bone marrow and circulate in the bloodstream in a quiescent state, but undergo 'explosive' activation upon damage to the vasculature, supporting formation of a vascular plug. Conditions associated with a reduction in platelet number (thrombocytopenia) or function can lead to excessive bleeding. Strikingly, platelets play a fundamental role in thrombotic disorders, including stroke and myocardial infarction, and are recognized as major pharmaceutical targets. Despite this clinical significance, there are major gaps in our understanding of the molecular events which underlie platelet formation and platelet activation. Research in this area has been hampered by the small size of the platelet and absence of a nucleus, and the low number of megakaryocytes in bone marrow and the challenge of growing these in vitro. The situation is beginning to change through availability of genetically-modified mice, discovery of thrombopoietin (the major cytokine regulating megakaryocyte growth and differentiation) and the introduction of powerful technologies such as proteomics and RNAi. The field is presently undergoing a revolution in terms of molecular progress. However, there is no focussed meeting that brings together scientists working on megakaryocyte and platelet cell biology for discussion of these issues. This is addressed through a new Gordon Conference on The Cell Biology of Megakaryocytes and Platelets'. This Conference will bring together academic and pharmaceutical investigators, post-doctoral fellows and graduate students for 5 days of intense discussion of the major scientific discoveries and challenges in the field at the Gordon Research Conference site in Rancho Santa Barbara on March 5-11th, 2005. This application is a request for partial funds to support the attendance of speakers and discussion leaders, and selected postdoctoral fellows and students at this important new meeting.